Question

With the NSUserDefaults class, you can save settings and properties related to application or user data.

now i have tow question :

1. ( settings and properties ) Where are stored ?
   if =>The objects will be saved in what is known as the iOS “defaults system”
   then : What is iOS “defaults system”

2. How long will remain stored ?

Answer 1

Where? It depends on what kind of app you’re developing. For AppStore applications, in the sandbox folder of your installed app folder, more precisely in the Library/Preferences folder. The actual file that contains the settings is a PLIST (property list) file whose name matches the bundle identifier of your app.

All in all:

(/var/mobile/Applications/XXXX-XXXX-XXXXXX-XXXXXXXX/MyApp.app/Library/Preferences/com.mycompany.bundleid.plist

(where XXXX etc. is an UUID).

If you’re making an app for jailbroken devices (i. e. a Cydia app), it will be a plist file again, whose name matches the bundle ID, but it will be installed in

/var/mobile/Library/Preferences/com.mycompany.bundleid.plist

The iOS defaults system is the part of the Foundation framework, iOS itself and the files and directories altogether which manage, store and modify your preferences/settings/defaults.

How long? Again, it depends on what kind of app you are writing. For a normal AppStore app, the defaults are persited to the file – but only as long as the user doesn’t delete your app. When your app is deleted, the whole sandbox, app bundle and od course the user defaults will also be gone. Forever, irreversibly.

If you develop a jailbroken application which resides in the system apps’ directory (/Applications), then the user defaults file will be available in /var/mobile/Library/Preferences even if the user deletes your package/application, as APT (the backing package manager of Cydia) only makes note of the files your package originally contained, and that’s not the case with the defaults property list file (which is only created when your app first accesses the NSUserDefaults class.) If the user manually deletes the file or restores to a stock firmware, it’ll be gone.